Antioxidants tied to mixed effects in breast cancer

Last Updated: 2011-10-07 15:32:02 -0400 (Reuters Health)

By Amy Norton

NEW YORK (Reuters Health) - Breast cancer patients who take antioxidants may have an increased or decreased risk of death or recurrent cancer, depending on which vitamin they use, a new study suggests.

Researchers found that among nearly 2,300 women with early-stage breast cancer, those who regularly used either vitamins C or E had a lower risk of cancer recurrence over five years than those who didn't use the vitamins.

On the other hand, women who regularly took a mix of carotenoids had a higher risk of dying from breast cancer, or any other cause, than women who did not take them.

Carotenoids include nutrients like vitamin A, beta-carotene and lutein.

The findings, reported in the journal Cancer, do not prove that any of the antioxidants are the reason for the effects seen.

But they do add to concerns about the risks of high doses of carotenoids, according to lead researcher Heather Greenlee, an assistant professor of epidemiology at Columbia University in New York.

"In my opinion," she told Reuters Health in an email, "our paper adds to the growing body of literature suggesting that dietary supplements containing high doses carotenoids may be harmful, and people should think twice before taking them."

Studies have found, for example, that giving beta-carotene supplements to smokers may actually raise their risk of lung cancer.

As for other antioxidants, Greenlee noted that the American Cancer Society and the American Institute for Cancer Research say that there's not enough evidence to recommend any dietary supplement for preventing cancer, or a cancer recurrence.

There is also concern about patients taking high doses of any antioxidant while on chemotherapy or radiation.

Antioxidants protect body cells from so-called oxidative damage. Cancer drugs and radiation work in part by creating oxidative damage. So in theory, high-dose antioxidants could diminish the treatments' effectiveness.

Still, studies show that women with breast cancer commonly use antioxidant supplements of some kind.

The current findings are based on questionnaires and case data from 2,264 U.S. women diagnosed with early-stage breast cancer.

Overall, 81 percent said they'd used at least one supplement containing antioxidants -- either within multivitamins or in the form of single-vitamin supplements -- in the two years after being diagnosed.

Over the next five years, the study found, women who'd reported using single supplements of either vitamin C or vitamin E six to seven days a week had a lower risk of cancer recurrence.

Of 540 women who took vitamin C, 15 percent had a breast cancer recurrence. That compared with 19 percent of the 1,072 women who did not use vitamin C supplements.

The differences were about the same when the researchers looked at vitamin E.

On the other hand, women who used any combination of carotenoids had a higher risk of dying from breast cancer, or from any cause. Of 89 women who used carotenoids six to seven days per week, 18 percent died of breast cancer; that compared with just under seven percent of women who did not use carotenoid combinations.

According to Greenlee, much of the benefit associated with vitamins C and E could potentially be explained by a "healthy user bias" -- that is, women who use dietary supplements tend to have healthier habits in general.

And that, she and her colleagues write, makes the increased risk of death linked to carotenoid use "even more striking."

The reasons for the different breast cancer outcomes linked to different antioxidants are not known, and the findings need to be confirmed in further studies, Greenlee said.

The most important point this study raises, she added, is that "antioxidant dietary supplements should not be assumed to all act in a similar fashion, as is a common perception in the general public."

"They are made up of different molecules," Greenlee said, "and likely have different effects."

On the other hand, the researchers found no evidence that breast cancer recurrence or deaths were linked to antioxidants taken within multivitamins -- which generally have more moderate doses of individual nutrients.